In recent years, prepregs in which reinforcing fibers are impregnated with a matrix resin are broadly used in various industrial fields. For example, sheet prepregs respectively obtained by paralleling a plurality of reinforcing fiber bundles respectively consisting of a plurality of paralleled single fibers such as carbon fibers or glass fibers, and impregnating them with a thermosetting resin such as an epoxy resin or unsaturated polyester resin, etc. are being widely used as general industrial materials such as aircraft materials and automobile materials, and also as medical materials and formed materials for sports and leisure like fishing rods, golf club shafts, badminton rackets, tennis rackets, etc.
Since the applications of prepregs are diversified like this, there are growing demands for thinner prepregs and prepregs using thermoplastic resins, and the necessity of improving the grade of prepregs, that is, producing more uniform prepregs with less thickness irregularity has grown. To meet these demands and requirements, it is necessary to open the reinforcing fiber bundle before impregnating it with a matrix resin when forming a prepreg, for reducing the thickness of the reinforcing fiber bundle and for letting the matrix resin sufficiently fill the clearances between the single fibers of the reinforcing fiber bundle.
In the production of a prepreg, one of the reasons why the opening of reinforcing fiber bundles is necessary is cost reduction. To produce a uniform and thin prepreg, generally thin reinforcing fiber bundles or reinforcing fiber bundles small in the number of component filaments are paralleled in one direction to produce a thin prepreg. However, since thin reinforcing fiber bundles or reinforcing fiber bundles small in the number of component filaments are generally expensive, it is advantageous to open reinforcing fiber bundles as thick as possible or as large as possible in the number of component filaments for forming a thin reinforcing fiber sheet and to manufacture a prepreg using the sheet. That is, if thick reinforcing fiber bundles or reinforcing fiber bundles large in the number of component filaments are opened to produce a thin prepreg with a conventional thickness, a desired prepreg can be produced at a lower cost.
Thus, the technique for efficiently opening the raw reinforcing fiber bundles is important among the techniques for producing a prepreg from reinforcing fiber bundles. As methods for opening reinforcing fiber bundles, for example, the following techniques are known.
(1) A method for feeding reinforcing fiber bundles at a speed of 0.04 m/s or less for letting them run on a round rod or revolving roll vibrated in the axial direction (Japanese Patent Laid-Open (Kokai) No. 56-43435) PA0 (2) A method for feeding reinforcing fiber bundles at about 1 m/s for letting them run on a roll vibrated in the revolving axis direction for vibrating the reinforcing fiber bundles with tension (an example described in Japanese Patent Laid-Open (Kokai) No. 2-36236). PA0 (3) A method for letting reinforcing fiber bundles run on several round rods or revolving rolls arranged at angles of 30 to 90.degree. (Japanese Patent Publication No. 3-31823) PA0 (4) A method for bringing a round rod ultrasonically vibrated in the axial direction into contact with reinforcing fiber bundles (Japanese Patent Laid-Open (Kokai) No. 1-282362) PA0 (5) A method for heating reinforcing fiber bundles for removing or reducing the sizing agent deposited in them (Japanese Patent Publication No. 3-25540) PA0 (6) A method for bringing a round rod heated to 50 to 200.degree. C. into contact with reinforcing fiber bundles (Japanese Patent Laid-Open (Kokai) No. 3-146735) PA0 (7) A method for opening reinforcing fiber bundles using a water stream (Japanese Patent Laid-Open (Kokai) No. 52-151362) and so on. PA0 (a) vibrating at least one of the plurality of rolls in the axial direction of the roll, PA0 (b) pressing the reinforcing fiber bundle onto the peripheral surface of a roll located immediately downstream of the vibrating roll, without vibrating the roll, and PA0 (c) bringing the reinforcing fiber bundle into contact with the peripheral surface of the non-vibrating roll with the contact length of not less than twice the contact length of the reinforcing fiber bundle on the peripheral surface of the vibrating roll. PA0 (a) a roll located immediately downstream of the vibrating roll vibrated by said exciting means, being not vibrated, and PA0 (b) said non-vibrating roll, having a peripheral surface with the contact length kept at not less than twice the contact length of the reinforcing fiber bundle on the peripheral surface of the vibrating roll. PA0 (a) the plurality of rolls, being provided as 2 to 10 pairs of rolls, each pair consisting of a vibrating free revolving roll vibrated in the axial direction of the roll and a non-vibrating free revolving roll, and PA0 (b) the diameters of the vibrating free revolving rolls in the respective pairs, being kept in a range of 20 to 50 mm, the diameters of the non-vibrating free revolving rolls, being kept in a range of 50 to 120 mm, and the distance between each of the vibrating free revolving rolls and its mating non-vibrating free revolving roll, being kept in a range of 10 to 100 mm as the length of the reinforcing fiber bundle segment not in contact with either of the rolls. PA0 (a) vibrating at least one of the plurality of rolls in the axial direction of the roll for opening the reinforcing fiber bundle(s), PA0 (b) pressing the reinforcing fiber bundle(s) to the peripheral surface of the roll located immediately downstream of the vibrating roll, without vibrating the roll, PA0 (c) bringing the reinforcing fiber bundle(s) into contact with the peripheral surface of the non-vibrating roll with the contact length kept at not less than twice the contact length of the reinforcing fiber bundle(s) on the peripheral surface of the vibrating roll, for retaining the opened state of the reinforcing fiber bundle(s) and PA0 (d) impregnating the reinforcing fiber bundle(s) with the opened state retained, with a resin. PA0 (a) arranging 2 to 10 pairs of rolls, each pair consisting of a vibrating free revolving roll vibrated in the axial direction of the roll and a non-vibrating free revolving roll, with the diameters of the vibrating free revolving rolls kept in a range of 20 to 50 mm, with the diameters of the non-vibrating free revolving rolls kept in a range of 50 to 120 mm, and with the distance between each of the vibrating free revolving rolls and its mating non-vibrating free revolving roll kept in a range of 10 to 100 mm as the length of the reinforcing fiber bundle segment not in contact with either of the rolls, and letting the reinforcing fiber bundle(s) run through the vibrating free revolving rolls and the non-vibrating free revolving rolls alternately, for opening the reinforcing fiber bundle(s), and PA0 (b) impregnating the opened reinforcing fiber bundle(s) with a resin. PA0 (a) a roll located immediately downstream of the roll vibrated by the exciting means, being not vibrated, and PA0 (b) the non-vibrating roll, having a peripheral surface with the contact length kept at not less than twice the contact length of the reinforcing fiber bundle(s) on the peripheral surface of the vibrating roll. PA0 (a) the plurality of rolls, being provided as 2 to 10 pairs of rolls, each pair consisting of a vibrating free revolving roll vibrated in the axial direction of the roll and a non-vibrating free revolving roll, and PA0 (b) the diameters of the vibrating free revolving rolls in the respective pairs, being in a range of 20 to 50 mm, the diameters of the non-vibrating free revolving rolls, being in a range of 50 to 120 mm, the distance between each of the vibrating free revolving rolls and its mating non-vibrating free revolving roll, being in a range of 10 to 100 mm as the length of the reinforcing fiber bundle segment not in contact with either of the rolls.
In such conventional methods, for example as shown in FIG. 6, the reinforcing fiber bundles 102 unwound from packages 101 to run in parallel to each other are fed through a comb 103, to be regulated in fiber bundle intervals, and pressed against a roller 105 vibrated in the axial direction by an excitation source 104, to rub the reinforcing fiber bundles 102 in the width direction for opening them.
Furthermore, the following techniques are also known.
However, the inventors found that even if any of the above prior arts is employed, if each reinforcing fiber bundle to be opened has its filaments entangled or remains twisted, the fiber bundle once opened on a vibrated roll has the filaments bundled again due to tension at a certain point downstream of the roll, returning the width of the fiber bundle to almost the same width as that before opening. If such fiber bundles are impregnated with a resin later, the prepreg obtained has portions not impregnated with the matrix resin and cannot be practically used. Furthermore, in the conventional methods of vibrating a roll as described above, the apparatus as a whole is heavily vibrated and cannot withstand the operation for a long time.
On the other hand, individual reinforcing fibers are generally given a sizing agent such as an epoxy resin, to be improved in handling convenience, for the reason that they are likely to be broken and frequently fuzzed since they are high in elastic modulus and small in diameter. The sizing agent functions as a "glue", to bond the single fibers mutually, and prevents the fiber bundle from being opened. Therefore, unless any means is taken to allow opening against the bonding strength of the sizing agent, the improvement of openability cannot be expected.
The above-described respective prior arts (1) to (7) are respectively examined below in more detail. The method (1) of feeding reinforcing fiber bundles at a speed of 0.04 m/s or less for letting them run on a round rod vibrated in the axial direction has a problem that if the reinforcing fiber bundles are driven to run at a high speed of 0.08 to 0.50 m/s, the reinforcing fiber bundles are abraded by the round rod, to be fuzzed. The method also has a problem that when a revolving roller is installed, the opened width is small usually when the reinforcing fiber bundle supply speed is high, not allowing the intended effect to be obtained.
The method (2) of feeding reinforcing fiber bundles at about 0.02 m/s for letting them run on a roll vibrated in the revolving axis direction for vibrating the reinforcing fiber bundles with tension has a problem that if the reinforcing fiber bundles are driven to run at a high speed of 0.08 to 0.50 m/s, the reinforcing fiber bundles are likely to be abraded more than in the above method (1) because of vibration with tension, being fuzzed more.
The method (3) of bringing reinforcing fiber bundles into contact with several round rods arranged at angles of 30 to 900 has a problem that if the reinforcing fiber bundles are brought into contact at a high speed of 0.08 to 0.50 m/s, abrasion causes fuzzing. Furthermore, the method has a problem of space since if revolving rolls are used, very many revolving rolls are necessary because of a small opening effect.
In the method (4) of bringing reinforcing fiber bundles into contact with a round rod ultrasonically vibrated in the axial direction, if the round rod is brought into contact with the reinforcing fiber bundles at a speed of 0.08 to 0.50 m/s, the opened width is small to decrease the effect. Furthermore, the method has a problem that the reinforcing fiber bundles are abraded by a round rod, to be fuzzed, since the round rod is vibrated ultrasonically.
In the method (5) of heating reinforcing fiber bundles for decreasing or removing the sizing agent deposited in them, the equipment for treating the sizing agent removed from the reinforcing fiber bundles is necessary to raise the equipment cost. Especially when the reinforcing fiber bundles are supplied at a high speed of 0.08 to 0.50 m/s, the heating zone must be longer, to further raise the equipment cost.
The method (6) of bringing reinforcing fiber bundles into contact with a round rod heated to 50 to 200.degree. C. has a problem that since the round rod is directly heated, the supply of reinforcing fiber bundles for a long time causes the sizing agent to stick to the round rod, to cause fuzzing.
The method (7) of opening reinforcing fiber bundles using a water stream has a problem of waste water treatment since the water containing the sizing agent must be discharged, raising the equipment cost. Furthermore, the equipment and energy for drying are necessary unpreferably in view of economy.